Particle-surface Interactions Research Articles

Predicting adsorption isotherms for methanol and water onto different surfaces using the SAFT-VR-2D approach and molecular simulation

In this work the statistical associating fluid theory for chain molecules with attractive potentials of variable range (SAFT-VR) and its two-dimensional version (SAFT-VR-2D) are applied to model thermodynamic properties of adsorption of water and methanol onto several types of adsorbents: activated carbons, metal organic frameworks (MOF) and carbon molecular sieve membranes. Fluid molecules are hard-spheres particles with square-well (SW) attractive interactions used to model particle-particle and particle-surface interactions. Associating interactions are described with two, three and four SW sites. Satisfactory results are obtained when compared with experimental data within a wide range of temperatures and pressures, including the reproduction of adsorption isotherms type V in the case of water. We include predictions for the relationship between mole fractions for adsorbed and bulk molecules, and how these properties are modified by the presence of association in both phases.

An investigation of the deposition of ceria on silica by quartz crystal microbalance: Observations on the effect of many body interactions

Interaction of ceria and silica is important in a wide variety of applications such as Chemical Mechanical Polish (CMP). In this work, a Quartz Crystal Microbalance (QCM) and mathematical modeling and simulations are used to investigate the dynamics of the attachment of ceria and silica under different flow rate, colloid concentration and pH conditions. The well-known DLVO forces of interaction were successfully used to distinguish between favorable and unfavorable conditions for the attachment of ceria and silica, and to develop a cleaning procedure to obtain reproducible data when using QCM for studying charged particles. The use of the optimized cleaning procedure as well as careful selection of the experimental conditions such as flow rate and concentration led to the important experimental observation that deposition of ceria particles onto silica surface is affected by many body particle–particle interactions in the bulk that can hinder the ability of the ceria particles to successfully attach to the silica surface. These experimental results could not be predicted by using a convection-diffusion-migration model which incorporates a single particle-surface DLVO interaction energy but ignores particle–particle interactions in the bulk. This is an important finding that permits the determination of the proper conditions for applications such as CMP and post CMP cleaning.

Optical Trap Loading of Dielectric Microparticles In Air.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

Pore‐network modeling of particle retention in porous media

Transport and filtration of micron and submicron particles in porous media is important in applications such as water purification, contaminants dispersion, and drilling mud invasion. Existing macroscopic models often fail to be predictive without empirical adjustments and a more fundamental approach may be required. We develop a physically‐representative, 3D pore network model based on a particle tracking method to simulate particle retention and permeability impairment in polydisperse particle systems. The model includes the effect of hydraulic drag, gravity, electrostatic and van der Waals forces, as well as Brownian motion. A converging‐diverging pore throat geometry is used to capture the mechanism of interception. With the analytical solution of fluid velocity within a pore throat, the trajectory of each particle is calculated explicitly. We also incorporate surface roughness and particle–surface interaction to determine particle attachment and detachment. Pore throat structure and conductivity are updated dynamically to account for the effect of deposited particles. Predictions of effluent concentration and macroscopic filtration coefficient are in good agreement with published experimental data. We find that the filtration coefficient is dependent on the relative angle between fluid flow and gravity. Particle deposition by interception is significant for large particle/grain size ratios. Brownian diffusion is the primary cause of retention at low Peclet numbers, especially for small gravity numbers. Particle size distribution is found to be a cause of hyperexponential deposition often observed in experiments. Permeability reduction was small for strong repulsive forces because particles only deposited in paths of slow velocity. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3118–3131, 2017

High pressure micromechanical force measurements of the effects of surface corrosion and salinity on CH4/C2H6 hydrate particle-surface interactions.

In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force (MMF) apparatus was applied to directly measure CH4/C2H6 hydrate adhesion/cohesion forces under low temperature and high pressure conditions. A CH4/C2H6 gas mixture was used as the hydrate former. Adhesion forces between hydrate particles and carbon steel (CS) surfaces were measured, and the effects of corrosion on adhesion forces were analyzed. The influences of NaCl concentration on the cohesion force between CH4/C2H6 hydrate particles were also studied for gas-dominated systems. It was observed that there was no measurable adhesion force for pristine (no corrosion) and corroded surfaces, when there was no condensed water or water droplet on these surfaces. With water on the surface (the estimated water amount was around 1.7 μg mm-2), a hydrate film growth process was observed during the measurement. CS samples were soaked in NaCl solution to obtain different extents of corrosion on surfaces, and adhesion measurements were performed on both pristine and corroded samples. The adhesion force was found to increase with increasing soak times in 5 wt% NaCl (resulting in more visual corrosion) by up to 500%. For the effect of salinity on cohesion forces, it was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model.

Thermal transport at a solid-nanofluid interface: from increase of thermal resistance towards a shift of rapid boiling.

We use molecular dynamics simulations to investigate interfacial thermal transport between an ethanol suspension containing gold atomic clusters and a gold surface, using both realistic and simplified molecular models of nanoparticles. The interfacial thermal conductance was determined via a thermal relaxation method for a variety of nanoparticle-nanoparticle and nanoparticle-surface interaction strengths. The Kapitza resistance is found to increase due to the presence of nanoparticles in the vicinity of the solid-liquid interface. The heat flow from the solid to the nanoparticles is separated from its counterpart from the solid to the liquid to discriminate their respective contribution to the total heat current. A per-vibrational-mode analysis highlights a shift of major heat carriers from low frequencies towards higher frequencies due to the coupling of the internal nanoparticle dynamics to the gold surface, in addition to stronger particle-surface interactions. Finally, we demonstrate that the increase of the Kapitza resistance significantly shifts the nanofluid/solid surface explosive boiling temperature to higher temperatures compared to pure ethanol.

Understanding How Charged Nanoparticles Electrostatically Assemble and Distribute in 1-D.

The effects of increasing the driving forces for a 1-D assembly of nanoparticles onto a surface are investigated with experimental results and models. Modifications, which take into account not only the particle-particle interactions but also particle-surface interactions, to previously established extended random sequential adsorption simulations are tested and verified. Both data and model are compared against the heterogeneous random sequential adsorption simulations, and finally, a connection between the two models is suggested. The experiments and models show that increasing the particle-surface interaction leads to narrower particle distribution; this narrowing is attributed to the surface interactions compensating against the particle-particle interactions. The long-term advantage of this work is that the assembly of nanoparticles in solution is now understood as controlled not only by particle-particle interactions but also by particle-surface interactions. Both particle-particle and particle-surface interactions can be used to tune how nanoparticles distribute themselves on a surface.

Quantitative Scanning Probe Microscopy for Nanomechanical Forensics.

Atomic force microscopy (AFM) was used to assess the indentation modulus Ms and pull-off force Fpo in four case studies of distinct evidence types, namely hair, questioned documents, fingerprints, and explosive particle-surface interactions. In the hair study, Ms decreased and Fpo increased after adding conditioner and bleach to the hair. For the questioned documents, Ms and Fpo of two inks were markedly different; ballpoint pen ink exhibited smaller variations relative to the mean value than printer ink. The fingerprint case study revealed that both maximum height and Fpo decreased over a three-day period. Finally, the study on explosive particle-surface interactions illustrated that two fabrics exhibited similar Ms, but different Fpo. Overall, it was found that AFM addresses needs in forensic science as defined by several federal agencies, in particular an improved ability to expand the information extracted from evidence and to quantify its evidentiary value.

Universal Diffraction of Atomic and Molecular Matter-Waves: A Comparison of He and D2 Quantum Reflected from a Grating.

Molecular beams of He and D2 are scattered from a ruled diffraction grating in conical-mount geometry under grazing-incidence conditions. Fully resolved diffraction patterns as a function of detection angle are recorded for different grating azimuth angles and for two different kinetic energies of the particle beams. Variations in diffraction peak widths are traced back to different velocity spreads of He and D2 determined by time-of-flight measurements. A comprehensive analysis of diffraction intensities confirms universal diffraction, that is, for identical de Broglie wavelengths, the relative diffraction intensities for He and D2 are the same. Universal diffraction results from peculiarities of quantum reflection of the atoms and molecules from the diffraction grating. In quantum reflection particles scatter many nanometers in front of the surface from the long-range attractive branch of the particle-surface interaction potential without probing the potential well and the short-range repulsive branch of the potential.

Chemically cleaning of UF membranes fouled by oily waste water.

The Ultra filtration membranes are used for treatment and reused of oily waste waters. The fouling of the ultra filtration membranes is caused due to inorganic and organic materials present in waste water that adhere to the surface and pores of the membranes and resulted in fouling and deterioration perforformance with increase in cost of energy and membranes replacement. In this experiment, Ultra filtration membranes fouling and cleaning were performed with oily waste water and selecting cleaning agents using laboratory scale cross flow membrane test unit. The result showed that the combination of cleaning agent that is metal chelating agent (Ethylene diamine tetraactetic acid) and an surfactant (sodium dodecyl sulfate (SDS) and sodium hydroxide were able to clean fouled membranes very effectively than the individual cleaning agent. The flux recovery percentage was found to improve with increasing cross flow velocity, temperature, pH and concentration of the cleaning solutions. Keywords-ultrafiltration; fouling; cleaning; surfactant; oily waste water. I. INTRODUCTION The fouling of membranes is typically caused by inorganic and organic materials that adhere to the surface and pores of the membrane and result in deterioration of performance (reduce flux of the membrane) with consequent increase in costs of energy and membrane replacement. A. Fundamental of Separation The forces of interaction between the membrane surface and particles in the solution are important in understanding the fouling phenomena. The normal basis for quantifying particle surface interaction is DLVO theory where the particle surface interactions in aqueous environments could be predicted by the summation of van der Waals and electrostatic double layer forces. Reducing the interaction between the particles and the membranes as much possible can reduce the fouling phenomena. This can be achieved when the critical value (flux and pressure) arises as a balance between the hydrodynamic force driving solute towards the pore and electrostatic forces opposing the motion. Critical flux stems from the concept that the higher the flux the stronger is the drag force towards the membranes. The stronger concentration polarization and higher the compaction of particles. Critical flux is defined as the limiting flux value below which a flux decline over time does not occur.(1).the number of parameter influenced this critical flux have been discussed in detail can be found(2).It is maintained that if one operates below the critical flux the fouling can be avoided or minimized. The fouling is common to all types of membrane separation. B. Fouling Membranes fouling are an extremely complex phenomenon that has not been defined precisely. In general the term used to describe the undesirable formation of deposits on membrane surfaces. This occurs when rejected particles are not transported from the surface of the membrane back to the bulk stream. The foul ant are typically colloidal materials of one types or another and their properties and interaction with membranes dominant fouling /cleaning processes. Colloids are defined as fine suspended particles in the size range of few nanometers to few micrometers. Examples of common colloids sizes foulant includes inorganic(clay, silica salt and metal

Simultaneous Characterization of Nanoparticle Size and Particle-Surface Interactions with Three-Dimensional Nanophotonic Force Microscopy.

The behavior of a nanoparticle in solution depends strongly on the particle's physical and chemical characteristics, most notably the particle size and the surface properties. Accurately characterizing these properties is critical for quality control in a wide variety of industries. To understand a complex and polydisperse nanoparticle suspension, however, ensemble averaging is not sufficient, and there is a great need for direct measurements of size and surface properties at the individual nanoparticle level. In this work, we present an analysis technique for simultaneous characterization of particle-surface interactions and size using near-field light scattering and verify it using Brownian-dynamics simulations. Using a nanophotonic waveguide, single particles can be stably held near the waveguide's surface by strongly localized optical forces. By tracking the dynamic 3D motion of the particle under the influence of these forces using an optical microscope, it is possible to extract the particle-surface interaction forces, as well as to estimate the size and refractive index of the nanoparticle. Because of the strong light-scattering signal, this method is viable for high-throughput characterization of particles as small as 100 nm in only a few seconds each.

Modelling of particle resuspension by a turbulent airflow and the role of particle size, surface roughness and electric charge

A resuspension model based on the Lennard–Jones intermolecular potential is applied to a monolayer deposit of spherical particles. The model considers the interactions between a particle and a surface under the influence of an external turbulent airflow. The particle–surface interaction was modelled with and without particle deformation due to elastic flattening. The resuspension rate was calculated by a kinetic force-balance approach whereby particle detachment occurs when the instantaneous joint contribution of the lift and drag forces exceeds the total adhesive force of the particle–surface system. Enhanced aerodynamic particle removal driven by the moment of the lift and drag forces was determined. Model predictions suggest that inclusion of the moment of the aerodynamic forces provides a suitable model for particle detachment (initiated by rolling). The importance of elastic deformation was found to depend on adhesive forces, characteristics of the substrate surface (surface roughness) and particle size. The model was applied to a number of laboratory experiments. For one set of experiments, we identified two resuspension regimes depending on whether small non-deformable or large deformable (equivalently, strongly or weakly bound) particles resuspended at high or low friction velocities. A modified model incorporating the effect of particle charge is also presented. Results indicate that particle resuspension is possible even when electrostatic forces are present, but the resuspension rate decreases considerably, depending on particle size, particle charge and surface roughness.

CMP Development for New Generation Materials through Metal Oxide Thin Film Characterization

Chemical Mechanical Planarization (CMP) process is currently facing the challenge to planarize larger scale wafers at an atomic scale precision. While the horizontal dimension (x-axis and y-axis as the wafer diameter) in the process can extend up to 300, 450 mm, the z-axis is limited to a margin of a couple hundred nanometers. This requirement highlights the need for fundamental understanding on the surface chemistry of the layers being exposed to the planarization process in terms of their interactions with the CMP slurry chemistry. Once the behavior of the wafer surface is understood at an atomic level, the process control metrics can be tuned accordingly. In our earlier work, we studied the growth of nano-scale protective oxide thin films for metal CMP on tungsten as a model [1]. Tungsten is a well-studied metallic layer in microelectronics and it is used as a gate dielectric for the novel T-gate transistors currently. Thin film analyses were conducted through advanced characterization techniques and also compared to the theoretical calculations for the modeling simulations. Atomic Force Microscope (AFM) was used to measure the surface roughness of the samples conditioned in the oxidizer environment before and after the CMP was conducted. The affect of surface roughness on wettability of the surfaces studied through contact angle measurements on the treated tungsten films. Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance FTIR/ATR technique in combination with the X-Ray Reflectivity (XRR) was utilized to determine the thicknesses of the oxidized nano films on the tungsten wafers. The results were evaluated through the comparison of the Pilling-Bedworth ratios of the oxidized nano films to determine the ability of the created oxide films as a self-protective oxide. Furthermore, a new modeling approach was introduced to CMP process optimization by means of topographic evaluation of the metal oxide thin films. Cahn Hilliard Equation (CHE) was utilized as an alternative to classical nucleation theory in terms of analyzing the topographic nature of the protective metal oxide nano films and modeling their growth, which was observed to affect the CMP performance [2]. It was concluded that the material removal rate mechanisms and the consequent planarization performance depend on the nature of nucleation of the metal oxide films, which is tailored by the oxidizer concentration. The basic knowledge defined on the chemically modified thin films has also been extended to the germanium CMP applications. Particularly, formation and selective removal of chemically modified germanium/silica thin films in the presence of cationic and anionic surfactants were evaluated through AFM wear tests as well as CMP and surface wettability responses. It was determined that while the self-assembled surfactant structures help improve slurry stability, they may retard the material removal rates by inhibiting the particle surface interactions [3]. The results of this study have shown that in the presence of hydrogen peroxide in the slurry, removal rates were mainly affected by the oxidizers surface activity resulting in the formation of germanium oxide film. However, surface quality and the selectivity of the Ge/SiO2 systems were tuned through adjusting the concentration of the oxidizer and surfactant type/chain length in the system to optimize the planarization performance [3]. This paper reviews the affects of chemically modified thin films on the CMP performance at an atomic level for tungsten, silica and germanium CMP applications as metal, dielectric and semiconductor materials utilized in the microelectronics industry. References A. Karagoz, V. Craciun, G.B. Basim, ECS Journal of Solid State Science and Technology, 4(2), 1 (2015). A. Karagoz, Y. Sengul, G.B. Basim, ECS Transactions, 61(17), 15 (2014).A. Karagoz, G.B. Basim, ECS Journal of Solid State Science and Technology, CMP Special Issue, 4(11), 5097 (2015).

Hopping on a wave: from periodic to chaotic transport

We study the dynamics of a particle on an elastic surface carrying a harmonic traveling wave. The particle–surface interaction is assumed to be inelastic both normally and tangentially, and the surface is assumed to provide a kinematic boundary condition to the particle. In this setting, we search for periodic hopping solutions of the particle. The results point to a rich variety of possible particle trajectories which include periodic and chaotic motions. Interestingly, coexisting distinct multi-period attractors, (one with period-3 and its multiples, and including coexisting periodic–chaotic attractors) are observed over a frequency band. In the case of a mutually non-interacting multi-particle system, we observe ballistic and diffusive transport in inter-leaved frequency bands. These results indicate tunability of transport without/with mixing.

Anti-soiling surfaces for PV applications prepared by sol-gel processing: Comparison of laboratory testing and outdoor exposure

Nanoporous SiO2 antireflective films and films additionally incorporating larger particles in this matrix were prepared by sol-gel processing; the latter exhibits a randomly corrugated surface pattern. Both films show a significant anti-soiling effect versus standardized test dust materials of different particle size distributions. The surface coverages determined by laser scanning microscopy were correlated to the respective optical properties. These laboratory results were compared to long-term outdoor exposure experiments performed in the Kingdom of Saudi Arabia. A vast potential of sol-gel derived coatings for anti-soiling applications is demonstrated, nevertheless the high complexity of the particle-surface interaction mechanisms cannot be underestimated.

Dynamics of an optically confined nanoparticle diffusing normal to a surface.

Here we measure the hindered diffusion of an optically confined nanoparticle in the direction normal to a surface, and we use this to determine the particle-surface interaction profile in terms of the absolute height. These studies are performed using the evanescent field of an optically excited single-mode silicon nitride waveguide, where the particle is confined in a height-dependent potential energy well generated from the balance of optical gradient and surface forces. Using a high-speed cmos camera, we demonstrate the ability to capture the short time-scale diffusion dominated motion for 800-nm-diam polystyrene particles, with measurement times of only a few seconds per particle. Using established theory, we show how this information can be used to estimate the equilibrium separation of the particle from the surface. As this measurement can be made simultaneously with equilibrium statistical mechanical measurements of the particle-surface interaction energy landscape, we demonstrate the ability to determine these in terms of the absolute rather than relative separation height. This enables the comparison of potential energy landscapes of particle-surface interactions measured under different experimental conditions, enhancing the utility of this technique.

A kinetic model for particle–surface interaction applied to rain falling on water waves

We present a model for estimating the momentum flux from water drops falling onto a moving free surface. The theory is based on a kinetic approach whereby individual drops are modelled as point particles with mass and velocity, and are described collectively by a distribution function $f(t,\boldsymbol{x},\boldsymbol{v},r)$. We show that the resulting momentum flux can be readily incorporated into free-surface Navier–Stokes and Euler models. As an illustration of this approach we examine the interaction between rainfall and linear deep-water surface waves. This particular application is not fundamentally different from the study of Le Méhauté & Khangaonkar (J. Phys. Oceanogr., vol. 20 (12), 1990, pp. 1805–1812), but our methodology is more general and is novel in its use of a kinetic approach with an all-purpose drop distribution function. The applicability of the model to linear surface waves is found to be valid for surface-wave wavelengths ranging from approximately 3 to 250 m. We further show that rainfall modifies the usual wave dispersion relationship and induces wave amplification, or damping, depending on the rain rate, the rain impact angle and the wavelength of the surface wave. We solve for the amplification and damping rates analytically and show, among other results, that rain falling vertically will always damp the surface waves.

Nanosecond Time-Resolution Study of Gold Nanorod Rotation at the Liquid-Solid Interface.

Early studies showed that the adsorption of nanorods may start from a special "anchored" state, in which the nanorods lose translational motion but retain rotational freedom. Insight into how the anchored nanorods rotate should provide additional dimensions for understanding particle-surface interactions. Based on conventional time-resolution studies, gold nanorods are thought to continuously rotate following initial interactions with negatively charged glass surfaces. However, this nanosecond time-resolution study reveals that the apparent continuous rotation actually consists of numerous fast, intermittent rotations or transitions between a small number of weakly immobilized states, with the particle resting in the immobilized states most of the time. The actual rotation from one immobilized state to the other happens on a 1 ms timescale, that is, approximately 50 times slower than in the bulk solution.

Metal Oxide Thin Film Characterization for New Generation Chemical Mechanical Planarization Development

This study targeted to create a basis for the new generation semiconductor industry that deals with atomic scale devices and also expected to be utilized in many other fields such as advanced coatings, interfacial adhesion, biological systems i.e. corrosion prevention and enhanced biocompatibility of bio-implants and nano/bio interfaces. We focused on the accomplishments on the microelectronics applications of the CMP process as it is used for the current and future semiconductor applications, such as metal CMP applications of the tungsten T-gate transistors, high speed shallow trench isolation transistors with germanium and furthermore isolating thin films for advanced microelectronics applications such as encapsulation of the PZT arrays of the ferroelectric memory applications. The second part focused on the applications of the CMP induced metal oxide thin films on biomaterials and conventional metals such as steel that is used for heating elements and aluminum that is being used for airplane bodies to improve the corrosion resistance. First of all, a fundamental understanding on the growth of nano-scale protective oxide thin films was studied to determine the effect of oxidizer type and proper oxidation time on the changes in surface properties of the thin films. The preliminary model was developed on the very well established tungsten, which is being utilized as a gate dielectric for the novel T-gate transistors currently. Thin film analyses were conducted through advanced characterization techniques and also compared to the theoretical calculations for the modeling simulations. Atomic Force Microscope (AFM) was used to measure the surface roughness of the samples conditioned in the oxidizer environment before and after the CMP was conducted. The affect of surface roughness on wettability of the surfaces studied through contact angle measurements on the treated tungsten films. Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance FTIR/ATR technique in combination with the X-Ray Reflectivity (XRR) was utilized to determine the thicknesses of the oxidized nano films on the tungsten wafers. The results were evaluated through the comparison of the Pilling-Bedworth ratios of the oxidized nano films to determine the ability of the created oxide films as a self-protective oxide [1]. Furthermore, a new modeling approach was introduced to CMP process optimization by means of topographic evaluation of the metal oxide thin films. Cahn Hilliard Equation (CHE) was utilized as an alternative to classical nucleation theory in terms of analyzing the topographic nature of the protective metal oxide nano films and modeling their growth, which was observed to affect the CMP performance. It was concluded that the material removal rate mechanisms and the consequent planarization performance depend on the nature of nucleation of the metal oxide films, which is tailored by the oxidizer concentration. The basic knowledge defined on the chemically modified thin films were also expanded to the germanium CMP applications. Particularly, formation and selective removal of chemically modified germanium/silica thin films in the presence of cationic and anionic surfactants were evaluated through AFM wear tests as well as CMP and surface wettability responses. It was determined that while the self-assembled surfactant structures help improve slurry stability, they may retard the material removal rates by inhibiting the particle surface interactions. The results of this study have shown that in the presence of hydrogen peroxide in the slurry, removal rates were mainly affected by the oxidizers surface activity resulting in the formation of germanium oxide film. However, surface quality and the selectivity of the Ge/SiO2 systems were tuned through adjusting the concentration of the oxidizer and surfactant type/chain length in the system to optimize the planarization performance [2]. References Karagoz, A., Craciun, V., Basim, G.B., “Characterization of Nano-Scale Protective Oxide Films_ Application on Metal Chemical Mechanical Planarization”. ECS Journal of Solid State Science and Technology, 4 (2) P1- P8 (2015)Karagoz, A., and Basim, G.B. “Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents”, ECS Journal of Solid State Science and Technology, CMP Special Issue, 4 (11) P5097-P5104 (2015).

Controlled Uniform Coating from the Interplay of Marangoni Flows and Surface-Adsorbed Macromolecules.

Surface coatings and patterning technologies are essential for various physicochemical applications. In this Letter, we describe key parameters to achieve uniform particle coatings from binary solutions. First, multiple sequential Marangoni flows, set by solute and surfactant simultaneously, prevent nonuniform particle distributions and continuously mix suspended materials during droplet evaporation. Second, we show the importance of particle-surface interactions that can be established by surface-adsorbed macromolecules. To achieve a uniform deposit in a binary mixture, a small concentration of surfactant and surface-adsorbed polymer (0.05 wt% each) is sufficient, which offers a new physicochemical avenue for control of coatings.